In one type of imaging infrared sensor system, a microelectronic light sensor is deposited on a substrate. The substrate is supported on a cold-finger pedestal. The other end of the pedestal is cooled by a gas-expansion cooler such as a Joule-Thomson cooler. The light sensor achieves its most efficient operation and highest signal-to-noise ratio when cooled to a cryogenic temperature such as liquid nitrogen temperature or lower. The light sensor and the cold-finger pedestal are placed inside a vacuum enclosure which has a window facing the light sensor and through which light is admitted. The vacuum enclosure insulates the light sensor and cold-finger pedestal, and protects the light sensor against physical damage.
When the sensor system is to be operated, compressed gas is passed through the gas-expansion cooler. Upon expansion through an orifice, the gas cools and absorbs heat to cool the cold-finger pedestal and thence the light sensor to a required temperature, typically a cryogenic temperature. Upon reaching the cryogenic operating temperature, the light sensor is activated. The output signal of the light sensor is provided to a display or to a computer for further processing.
Microelectronic sensor systems of this type are well known and widely used. One of their drawbacks, however, is that the time required to cool the light sensor from room temperature to its cryogenic operating temperature may be on the order of one minute. For some applications, that cooldown time may be acceptable, but for other applications, such as military applications, it may be unacceptably long. Additionally, the light sensor is cantilever mounted on the end of the cold-finger pedestal, increasing the susceptibility of the signals to degradation due to vibration. There is also the desire to decrease the size and weight of the sensor system as much as possible.
Various techniques have been employed to increase the cooldown rate and to reduce the size and weight of the sensor system. However, there remains a need for an improved approach to cryogenically cooled sensor systems that overcomes the cooldown rate, size, and weight shortcomings of prior coolers, while still providing the required low operating temperature and satisfactory performance of the light sensor.
This cooling problem has been posed in relation to sensors, but it is equally applicable to some other types of microelectronic systems that generate large amounts of heat during service, such as high-performance computer chips and microelectronic amplifiers. It may not be necessary to cool these microelectronic systems to cryogenic temperatures, but accelerated heat removal may be required to maintain the microelectronic systems within operating temperature limits.
Thus, there is a need for an improved approach to cooling a variety of microelectronic and other systems, some to cryogenic temperatures. The present invention fulfills this need, and further provides related advantages.